Musnad Abu Ya'la al-Mawsili 105:26

Ibrahim ibn al-Hajjaj narrated to us, Hammad narrated to us, from Ali ibn Zayd, from Salamah ibn Muhammad ibn Ammar ibn Yasir, from Ammar ibn Yasir, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Indeed, from the *fitrah* (natural disposition) are: rinsing the mouth, sniffing water into the nose, trimming the mustache, using the *siwak* (tooth stick), washing the knuckles, plucking the armpit hair, shaving the pubic area, circumcision, and sprinkling water (on the private parts after urination)."